Conversion of hydrocarbons



P 16, 1953 H. z. MARTIN I ET'AL 2,852,441

CONVERSION OF HYDROCARBONS 2 Sheets-Sheet 1 Filed Oct. 22. 1954 mmbqwr mOhO um H. z. MARTIN ETAL 2,852,441

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mum omm R h m3? 2.8 -62 \HNQ 55513. 5595 wnw 9N 2N F NNN t t $3 No Homer Z. Martin James W. Brown United States Patent CONVERSION or HYDROCARBONS Homer Z. Martin, Cranford, and James W. Brown, Elizabeth, N. J., assignors to Esso Research and Engineer iug Company, a corporation of Delaware Application October 22, 1954, Serial No. 464,049

7 Claims. (Cl. 196-49) This invention relates to the conversion of hydrocarbons and more particularly relates to a combination refining process including catalytic cracking of a distillate stock and cracking of the crude residuum.

In combination processes where a crude petroleum oil is separated into fractions and the higher boiling fractions and residues are cracked, there is a problem of heat balance especially where the residue is cracked or visbroken and the vaporous reaction products sent directly to the catalytic cracking reactor. In such combination designs heretofore an excess of heat has occurred in the catalytic cracking unit while there has been a deficiency of heat in the bottom of the combination fractionation tower.

According to this invention the crude petroleum oil is preheated preferably by indirect heat exchange with various oil streams and the virgin naphtha is then flashed off and passed directly to the catalytic cracking reactor without condensing or cooling the flashed naphtha. In this way heat is removed from the catalytic cracking unit instead of removing heat from the bottom of the fractionating tower. In addition, the virgin naphtha is reformed while passing through the catalytic cracking unit. In the preferred form of the invention a single combination fractionating tower is used for fractionating all of the cracked products and at least part of the crude petroleum oil. Bottoms from the combination tower are passed to a coking unit or catalytic cracking unit or such bottoms plus flashed crude oil bottoms may be cracked or coked.

In one form of the invention using the flashed naphtha, the bottoms from the common fractio-nating tower are coked and the coker overhead products passed to the catalytic cracking unit with heavy distillate oil stock from the common fractionating tower. Hot regenerated cata lyst is also introduced into the catalytic cracking unit. The flashed naphtha is passed to the catalytic cracking unit along with the rest of the feed stock to absorb some or" the excess heat in the cracking unit. By removing the flashed naphtha in this way and in passing it to the fractionating tower less heat is required for vaporizing hydrocarbons in the bottom of the fractionating tower.

In another form of the invention two catalytic cracking units are used, one for the crude oil and/ or bottoms from the common fractionator and the other cracking unit is used for the heavy distillate oil fraction withdrawn from the common fractionating tower. The total cracked products from the catalytic cracking unit are passed to the bottom of the fractionating tower for supplying heat to the fractionating tower and to aid in the fractionation of the various hydrocarbons. With the present invention better utilization of heat is obtained.

In the drawings:

Fig. 1 represents one form of apparatus which may be used in carrying out the invention; and

Fig. 2 represents another form 'of apparatus for carrying out the present invention.

Referring now to Fig. 1 of the drawings, the reference 2,852,441 Patented Sept. 16, 1958 ice character 19 designates a feed line through which the crude petroleum oil is passed. For preheating the crude oil it is passed through the first indirect heat exchanger 12 and a second indirect heat exchanger 14 to raise the crude -oil to a temperature sufliciently high to vaporize the virgin naphtha in the crude oil. The preheated oil then passed to a flash drum 16 where the naphtha is flashed overhead and withdrawn through line It; for passage to the catalytic cracking unit 22 to be hereinafter described in greater detail. The bottoms from the flash drum 16 are withdrawn through line 24- and introduced into the top of the shed section 26 of the common fractionating tower 28. Vaporous cracked products from the catalytic cracking unit 22 are passed through-line 32 into the bottom portion of the fractionating tower 28 below the shed section.

The cracked products are at a relatively high temperature and they supply heat to the bottom of the fraction ating tower 2.8. As they pass upwardly through the shed section 26 they contact the downwardly flowing residual oil or bottoms introduced into the top of the shed section 26 from line 24 so that fractionation of the cracked products and the bottoms occurs. The vapors leaving the shed section 26 are passed upward through the fractionating tower and are iurtherfractionated into desired fractions as will be presently described.

Returning to the first heat exchanger 12, the heat for the crude oil passing through line 10 is supplied by indirect heat exchange of hot oil withdrawn from the upper portion ofthe tower 23 through line 34 by pump 36.

After passing through the heat exchanger 12. the oil is passed through cooler 36 and returned to the upper portion of the fractionati'ng tower Zti'aboVethe plates therein.

The oil withdrawn through line 3 and cooled by the heat exchanger is returned to the top of the tower as reflux. I

Referring again to the second indirect heat exchanger 14, heat is supplied to the preheated crude oil passing through line 10 by a relatively heavy distillate oil fraction, such as gas oil withdrawn from trapout tray 38, and passed through line 42 by pump 44 and then through the indirect heat exchanger 14 via line '46. Part or the oil after passing through the heat exchanger '14 may be 'et'urned to the tower 28 through line '48 to about the middle portion of the fractionation tower 28 above trapout tray 38. Another portion of the oil from line 46 after passing through heat exchanger 14 may be passed through line 52 as part of the gas oil'feed passing toth'e catalytic cracking unit 22. Instead of passing all of the withdrawn oil through line 46 and heat exchanger 14, part of the oil may by-pass heat exchanger 1'4 and be passed through line 54 through line '55 directly'to the catalytic cracking unit.

Line 52 is provided with a control valve 53 so as to regulate the temperature of the feed'to reactor 22 and thus keep the reactor in heat balance. The waste heat boiler 53 controls the temperature of the drawoli tray 38 by removing heat from the tower. For removing an additional amount of heat from the distillate oil fraction withdrawn from trapout tray 38, a portion of the oil withdrawn through line 42 may be pas'sedthrough line 56 and waste heat boiler 58 and'th'e cooled oil fraction then passed to line '48 for re-introduction into the combination fractionating unit 28.

As above pointed out, the vapors passing upwardly through the fractionating tower 28 are separated into fractions including a distillate oil fraction such as gas oil (boiling range about 540-1000 P.) which is withdrawn from trapout tray 38. The gas oil fraction contains virgin and cracked constituents. Further up the tower a heating oil fraction (boiling range about 430 580 F.) may be withdrawn through line"62. The lightest boiling fraction which comprises the naphtha or "gaso- 'line 84 leading to the catalytic cracking unit 22.

3 line fraction (C 430 F.) is withdrawn overhead through line 64 and passed through cooler or condenser 66 and further treated as desired to recover the gasoline or naphtha.

The bottom of the fractionating tower 28 is provided with a tar pot 68 into which steam is introduced through line 72 to strip out volatile constituents from the bottoms Withdrawn from the bottom of the fractionating tower 28. The stripped bottoms (initial boiling point about 1100 F.) are withdrawn from the tar pot 68 and passed through line 74 by pump 76 to a cracking unit 78. This cracking unit 78 will be described as a fluid coking unit but other forms of coking may be used and also other cracking processes may be used for cracking the heavy bottoms. The fluid coking reactor 78 is of conventional design wherein the residual oil or-bottorns are cracked at a temperature between about 850 and 1050 F, preferably 950 F.

The fluid coke particles in the coking unit have a size of about 20 to 500 microns and fluidizing gas, such as steam or the like, is preferably passed upwardly through the fluid coker to maintain the particles in a dense turbulent fluidized condition. The superficial velocity of the upflowing gas and vapors in the coking unit 78 may be between about /2 and 4 feet per second, preferably about 1 to 3 feet per second.

The coking reactor '78 is utilized to upgrade residua or bottoms to form more gas oil feed for catalytic cracking with a minimum fonnation of gasoline and lighter products. About 10% to 20% by weight of gasoline is formed.

The density of the dense fluidized bed in the coker 78 is about 30 to 60 lbs. per cubic ft. The weight of oil per hour per weight of solids (w./hr./w.) in coking unit 78 may vary between about 0.1 and 5.

The hot vaporous cracked products pass overhead from the coking unit 78 through line 82 and are passed into In order to supply heat to the coking unit, coked particles are withdrawn from the bottom of the coking unit 78 through line 86, mixed with air introduced through line 88 and the resulting mixture passed to the heater or burner 92 wherein the coke particles are at least in part burned while they are maintained in a dense fluidized turbulent bed. The hot combustion gases pass overhead through line 94. In the heater the temperature is maintained between about l050 and 1500 F., preferably about 1125 F. and the coked particles heated to this temperature are withdrawn through line 96, mixed with a fluidizing gas, such as steam, from line 98 and the hot coked particles introduced into the coking unit 78 through line 102. Coke product is withdrawn through line 103. The superficial velocity of the upflowing gas in heater 92 may be between about 1 and 5 ft. per second and the density of the fluidized bed in the heater may be between about 30 and 60 lbs. per cu. ft.

The coking unit and heater associated therewith are shown diagrammatically and it will he understood that separating devices, such as cyclone separators, are used for separating entrained solid particles from the vaporous products passing overhead from the coking unit 78 and from the combustion gas passing overhead through line 94 from the heater. Instead of having a dense bed heater .or combustion zone, a transfer line heater may be used in which case the superficial velocity of the upflowing gas may be between 40 and 100 ft. per second and the density of the suspension passing through the transfer line heater may be between about 0.1 and 1 lb. per cu. ft. If desired, additional heat may be supplied to the heater or combustion zone by burning fuel in the combustion zone 92. Instead of using a fluid coking unit, other coking processes such as delayed coking or coking processes using compact moving beds .of inert solids or coke particles may be used. Also standpipes for circulat- 4 ing solids between the coker and heater are used as is well known in the cracking art.

Returning now to the catalytic cracking reactor 22 there are shown diagrammatically reactor 22 and regenerator 104. While it is preferred to use the fluid catalyst technique in the catalytic cracking unit, other forms of catalytic cracking units may be used, such as the fixed bed process or the moving compact bed process. The catalytic cracking unit is conventional and will not be described in great detail. It is to be understood that when using finely divided cracking catalysts, such as conventional synthetic silica alumina of a size of about 20 to microns, that standpipes will be provided for circulating the catalyst particles between the reactor and regenerator. Any known cracking catalysts may be used, such as silicaalumina, silica-magnesia, si1ica-alumina-nragnesia, acid treated bentonitic clays and so forth. The temperature in the catalytic cracking unit 22 will be between about 850 and 1050 F., preferably 950 F. The oil feed line 84 leading to the cracking unit 22 contains the hot vaporous cracked products passing overhead from the coking unit 78 through line 82, the flashed virgin naphtha passing through line 18 and the relatively heavy distillate oil fraction withdrawn from the trapout tray 38 through line 42 and passing through line 55 and hot regenerated catalyst from the regenerator 104. The superficial velocity of the vapors and gases passing upwardly through the catalytic cracking unit 22 is between about 1 and 3 feet per second, preferably 2 feet per second and the density of the dense fluidized bed in reactor 22 is between about 20 and 40 lbs. per cu. ft. The w./hr./w. in reactor 22 may be between about 2 and 6. The hot cracked vaporous products are taken overhead from the reactor 22 and passed through line 32 into the bottom of the fractionating tower 28 as above described. The vaporous cracked products are at a temperature of about 850- 1050 F. or about the temperature of the cracking unit During the cracking operation, carbonaceous material is laid down on the catalyst particles and they are regenerated by being withdrawn from the reactor 22, mixed with air introduced through line 106 and passed through line 108 to the regenerator 104 where the temperature is maintained between about 950 and 1200 F., preferably 1125 F. The hot combustion gases pass over head through line 112 and are preferably passed througl a waste heat boiler to recover heat therefrom. Hot regenerated catalyst is withdrawn from the regenerator 10% through line 114 and then passed through line 84 where the hot regenerated catalyst is mixed with the feed streams going to the catalytic cracking unit 22. The superficial velocity of the gas flowing up through the regenerator 104 is between about 1 and 4 ft. per second and the density of the dense fluidized bed in the regenerator is between about 20 and 40 lbs. per cu. ft. The reactor and regenerator are provided with dust separating means, such as cyclone separators or the like to separate entrained solid particles from the gases or vapors leaving the reactor and regenerator.

Referring now to Fig. 2, crude petroleum oil is passed through line 122, through indirect heat exchanger 124 to preheat the oil to a flashing temperature and the preheated oil is then passed through line 126 to flash drum 128 from which the flashed naphtha is taken overhead through line 132 and passed to the catalytic cracking unit 134 as will be hereinafter explained in greater detail. The bottoms from the flash drum 128 are withdrawn and passed through line 136 by pump 138 through a second heat exchanger 142 and then through a third heat exchanger 144. Preferably only a portion of the bottoms is passed through the heat exchanger 142 with the rest of the bottoms passing through line 146 and 148 to the top of the shed section 152 of the fractionating tower 154. Bottoms are withdrawn from the bottom of the fractionating tower 154 from tar pot 156 through line 158 by pump 162 and admixedwith the portion of the flashed bottoms from drum'128-after passage through the third heat exchanger 144 in line 164.

The combined bottoms stream is passed through line 166 and heater 168 and then passed through 1ine'172 to a second catalytic cracking unit 174 presently to be described in greater detail. For supplying heat to the crude petroleum oil and the bottoms from the flash drum 128 a relatively heavy distillate oil fraction, such as gas oil, is withdrawn from trapout tray 176 and passed through line 178 by pump 182, through the indirect heat exchanger 142 and then indirect heat exchanger 124 and then returned by line 184 to the fractionating tower 154 a distance above the trapout tray 176. For removing additional heat from this heavy distillate oil fraction withdrawn through line 178 there is provided a waste heat boiler 186 in by-pass line 188 for indirect contact with a portion of the heavy oil distillate passing through line 188. The cooled oil is returned to the tower via line 184. For supplying heat to the indirect heat exchanger 144, hot bottoms having an initial boiling point of about 1100 -F. are withdrawn from the bottom of the fractionating tower 154 through line 192 and passed through heat exchanger 144 and waste heat boiler 194 and returned to the bottom portion of the fractionating tower 154 above the shed section 152 through line 148. It will be noted that at least a part of the bottoms from the flash drum 128 passing through line 146 are mixed with the bottoms withdrawn through line 192 from the tower 154 downstream of waste heat boiler 194 and this mixture returned to the tower through line 148.

As above pointed out, the'fractionating tower 154 is provided with a tar pot 156 into which steam is introduced through line 196 for stripping out volatile material from the bottoms before they are withdrawn from the tar pot 156.

The hot vaporous cracked products passing overhead from the reactor 134 through line 202 and overhead from catalytic cracking reactor 174 through line 204 are combined and'passed through line 206to 'the bottom "of the fractio'nating tower 154 below 'the'shed section 152. The hot vaporous products supply heatito the-bottom of the fractionating tower and assist'in the fractionation of the vapors and in the stripping of volatile material from the crude oil and residualoil 'introduce'd through line 148 above the shed sectionf152.

As the vapors passupwa'rdly throu'gh the fractionating tower they are further fractionated :into the'heavy distillate fraction, such as gas "oil, which is "withdrawn from trapout tray 176 and higher up "in the tower a lighter fraction, such as heating oil, is separated and withdrawn through line 206. To supply reflux for the top of the fractionator tower154 a lighter fraction is withdrawn an'dpassed through line 208 bypump 21-2 and through heat exchanger 214. The cooled lighter 'oil is returned to the top of the tower'through line 216. The vaporous overhead fraction is withdrawn through line 218 and passed through'cooler 222 to recover gasoline or naphtha.

As feed for the catalytic cracking unit 134, aheavy distillate oil fraction, such as. gas oil, is withdrawn from trapout tray 176 and passed through line224 by pump 226. This gas oil fraction contains virgin .and cracked constituents. Also introduced into the catalytic cracking unit 134 is the hot flashed naphtha passing overhead from flash drum 128 through line 132. The naphtha is reformed in passingthrough catalytic cracking'unit 134 and has its octane number raised. The catalyst in the cracking unit 134 is the more active catalyst because the feedstock is relatively free of contaminants, whereas the catalyst in theother catalytic cracking unit 174 is less active because 'it is used for crackingresidual oil containing catalyst contaminating substances.

As catalyst in the cracking unit 134, a standard high activity synthetic silica alumina is preferably used but other high activity cracking catalysts, such as those above mentioned may be used. I The partially spent catalyst from cracking unit 134 is withdrawn from the reactor to line 226' and mixed with air introduced through line 228 and the mixture passed to a regenerator 232 in which the catalyst particles are maintainedas a dense turbulent fluidized mass or mixture. The temperature in the cracking unit 134 may bebetween about 850 and 1050 F., preferably 950F. The w./hr./w. in reactor 134 is between about 1 and 6. The temperature in the regeneration zone 232' may be between about 1000 and 1250 F, preferably 1125 "F. The hot combustion gases are taken overhead from the? regeneration zone 232 through line 234. Hot regenerated :catalyst is withdrawn from the regeneration zone 232 through line 236 and mixed with the feed passing through line 238 to the catalytic cracking unit 134.

.The catalyst in the second cracking unit 174 is used for cracking bottoms and residuum oil and, therefore, is of poorer quality than that used in the other reactor 134 and has a cracking-activity of about 12-20% D+L. For D+L see Ind. Eng. Chem. v. 39, p. 1140 (1947).

The w./hr./w. in reactor 174 is between about 4 and 12. The cracking in-second catalytic cracking unit 174 is preferably carried outunder milder conditions than in the first catalytic cracking unit 134 to crack high boiling constituents to' gas oil constituents rather than gasoline.

In this way, more feed-stock to catalytic cracker 134 is produced. About 10m 30% by-wt. on feed of gasoline is produced inreactor-174 and this gasoline has a relatively high octane number which is much higher than the gasoline produced-when visbreaking residual oils. Gas

formation is moderate. Coke formation is high but only because of the high-Conradson carbon content of the feed and not the cracking severity.

Catalyst used in reactor 174 preferably also comprises silicaalumina or the other catalysts above mentioned and instead of using fresh silica alumina catalyst in this reactor 174, spent catalyst or used catalyst may be withdrawn from the cracking unit 134 or other catalytic cracking units and used as the catalyst in the second cracking unit 174. Activated natural clays may be used. The finely divided catalystparticles in both units 134 and 174 are of a size'between about 10 and microns and the superficial velocity of the gas or vapor passing through the reactor and regenerator in these two units is between about-l and 4 feet per second, preferably 2 to 3 feet per second. The density of the dense fluidized beds in reactor 134 and regenerator 174 is between about 20 and 40 lbs. per. cu. ft.

Catalyst containing carbonaceous deposits is withdrawn from cracking unit 174 through line'242, mixed with air introduced through line 244 and the mixture passed through line 246 to the second regenerator 248 wherein the catalyst particles are maintained as a dense turbulent mass or mixture. Hot combustion gases are passed overhead through line 252. Hot regenerated catalyst is withdrawn fromthe regenerator "'248 through line 254 and mixed with preheated crude oil and residual oil leaving furnace 168 and the resulting mixture passed through line 172 to the catalytic cracking reactor 174. Standpipes for circulating the catalyst and cyclone separators or the like are used'as is conventional in the art. Waste heat boilers may be provided for recovering heat from the hot combustion gases leaving 'reg'enerators 232 and 248.

As a specific example, for cracking 53 ,800 barrels per day of a desalted crude oil made up of about 50% East Texas crude oil and 50% West Texas crude oil and at a temperature of about 100 F., the crude oil is passed through line 10 and then through heat exchanger 12 where its temperature is raised to about 250 F. The preheated crude oil is then passed through heat exchanger 14 where itstemperature is raised to about 545 F. The preheated oil under a pressure of about 100 lbs. per sq. in. gage (p. s; i. g.)1isthen passed'to the naphtha flash drum 16 where about 17,000 barrels per day of virgin naphtha at a temperature of 510 F. are flashed 011 by reducing the pressure from about 100 p. s. i. g. in line 10 ahead of the flash drum to about 50 p. s. i. g in flash drum 16. The flashed naphtha is passed through line 18 to the catalytic cracking unit 22.

Gas oil withdrawn from trapout tray 38 at a tempera ture of about 635 F. is passed through line 42 and a portion thereof passed through indirect heat exchanger 14 and the rest passed through line 54 so that the combined stream of the oil passing through line 55 and including that passed through the heat exchanger 14 and that by-passing the heat exchanger 14 in line 54 has a temperature of about 620 F. About 36,120 barrels per day of gas oil feed are passed through line 55 as part of the feed going to the catalytic cracking reactor 22. This gas oil feed contains both virgin and cracked gas oil.

In this specific example the catalytic cracking unit 22 is at a temperature of about 950 F. and has a catalyst holdup of about 110 tons. The catalyst is synthetic silica alumina containing about 13% alumina. The catalyst has a size of about 20 to 100 microns. in reactor 22 is about 4. The amount of coke made and deposited on the catalyst particles is 7.55% by weight of the total gas oil feed going to the catalytic cracker 22 and the total gas oil feed is about 45,340 barrels per day.

In the regenerator 104 there is a hold up of about 139 tons of catalyst and about 27,400 tons of coke are burned per hour. The regenerator is at a, temperature of about 1125 F. The density of the dense turbulent fluidized mass of catalyst in the reactor is about 35 lbs/cu. ft. and in the regenerator about 30 lbs./cu. ft. The catalytically cracked vaporous products taken overhead through line 32 are at a temperature of about 950 F. and are introduced into the bottom of the fractionatiug tower 28 below the shed section 26. The bottoms from the flash drum 16 having an initial boiling point of about 380 F. are withdrawn through line 24 at a temperature of about 510 F. and comprise about 36,800 barrels per day. This bottoms fraction is introduced into the bottom portion of the fractionating tower 28 above shed section 26. The temperature in the fractionating tower 28 above the shed section is about 740 F. There are withdrawn from the bottom of the fractionating tower 28 10,500 barrels per day of residuum which is passed through line 74 to the coking unit 78. The residuum has an initial boiling point of about 1000 F. The coking unit 78 has a hold up of 16.7 tons of cokeaud is maintained at a temperature of about 950 F. The space velocity or w./hr./W. in coking unit 78 is about 2.0. cracked or coked products passing overhead "from the coking unit through line 82 are at a temperature of about 950 F. and contain about 15% by weight of C 430 F. gasoline. The amount of cracked liquid products passing overhead through line 82 from the coking unit 78 is about 10,000 barrels per day. About 76 tons of coke per The hot The w./hr./w.

day is withdrawn through line 103. About 32,000 barrels per day of C 430 F. gasoline are produced in this process. About 14,870 barrels per day of heating oil are produced.

In this example the whole crude oil is converted to useful products including gas, gasoline heating oil and coke and there is no residual oil or tar to dispose of. The residual oil is cracked to extinction.

The oil feed to the catalytic cracking unit 22 comprises gas oil feed in line at 635 F., hot coker products at 950 F. and hot regenerated catalyst at 1125 F. and from this it will be seen that too much heat will be present in reactor 22 unless some heat is removed. That is the reason for adding the flashed naphtha at about 510 F. to remove heat from reactor 22 while at the same time some reforming of the virgin flashed naphtha is efiected by passage through the catalytic cracking unit 22 at 950 F. If, instead of flashing the naphtha, the preheated crude oil were introducedinto the lower'portion of the fractionating tower 28, the temperature in the lower part of the tractionating tower 28 would be lowered and heat would have to be supplied to the crude oil by a heating furnace or the like before introducing it into the tower 28. This heating furnace is eliminated by using the present process.

In the form of the invention shown in Fig. 2, the crude petroleum oil of the same composition as that used in the example for Fig. 1 is preheated to a flashing temperature by passing through the heat exchanger 124 where heat is supplied by the hot stream of oil Withdrawn from the trapout tray 176 in the tower 154. The crude feed oil has its temperature raised from about 100 F. to 485 F. and using about 53,800 barrels per day of the crude oil as the starting feed about 14,150 barrels per day of virgin naphtha at a temperature of 450 F. are recovered from the flash drum 128 and passed through line 132 to the catalytic cracking unit 134 maintained at a temperature of about 950 F.

Bottoms from the flash drum 128 are withdrawn at a temperature of about 450 F. and a portion thereof passed through heat exchangers 142 and 144 to raise the temperature of the flash drum bottoms to about 650 F.

About 5500 barrels per day of tower bottoms are withdrawn from the bottom of the tar pot 156 of tower 154 at a temperature of about 700 F. and are admixed with the heated fla'sh drum bottoms from heat exchanger 144 to give a stream having a temperature of about 660 F. The heated bottoms stream from heat exchanger 144 comprises about 29,480 barrels per day. The portion of the bottoms from flash drum 128 by passing heat exchanger 142 and passing through line 146 comprises 10,170 barrels per day and is at a temperature of about 450 F. The bottoms stream'withdrawn through line 192 and passing through heat exchanger 144 and waste heat boiler 194 is at a temperature of about 750 F. before passage through the heat exchanger and has its temperature reduced to about 500 F. and is then returned to the top of the shed section 152 through line 148.

The gas oil feed withdrawn from trapout tray 176 through line 224 comprises about 30,000 barrels per day and is at a temperature of about 600 F. but when it is mixed with the flashed naphtha at 450 F. the temperature of the combined stream going to cracking reactor 134 via line 238 is about 550 F. The combined bottoms stream passing through line 166 has its temperature raised to 750 F. by passage through the preheating furnace 168.

The catalyst used in cracking reactor 134 is of the same size and composition as that described for reactor 22 in Fig. 1 and has a D+L cracking activity of about '30. The catalyst holdup in reactor 134 is about 93 tons. The w./hr./w.' in reactor 134 is about 4. The amount of coke produced is about 6.0 wt. percent on the total liquid oil feed to reactor 134. In regenerator 232, the temperature is about 1125 F., the catalyst hold up is about 123 tons and the superficial upflowing gas velocity is 2.7 feet per second. About 24,400 lbs. of coke are burned per hour. The regenerated catalyst from r;-

The' catalyst used in the other catalytic cracking unit 174 contains used silica-alumina catalyst having about 1 down on the catalyst.

the same particle size and composition as above given for reactor 134. This catalyst has a D+L cracking activity of about 15-20. The catalyst hold up in reactor 174 is about 30 tons, the temperature is about 950 F. and the superficial velocity of the upfiowing gasiform material is about 20 feet per second. About 2.63 wt. percent of coke on liquid oil feed to reactor 174 is laid In regenerator 248 the catalyst hold up is about 61 tons, the temperature is about 1125 F. and the: superficial velocity of the upflowing gas 1s about 2.7 'feetper second. The w./hr./w. in reactor 174 is about 2 It will be seen from this example that much less coke is made in reactor 174 than in reactor 134.

The total cracked products passing through line 206 are at a temperature of about 950 F. The bottom of the shed section 152 is at temperature of about 740 F. The top of the shed section 152 is at a temperature of about 700 F. About 32,000 barrels per day of C 43O F. gasoline are recovered from the overhead products passing through line 218. About 14,870 barrels per day of heating oil are re... -ed through line As in the first example, the whole crude in this example is also cracked to extinction with no residual oil or tar to be disposed of.

The hot regenerated catalyst passing through line 254 for admixture with bottoms oil or residuum from line 166 is at about 1125" F. If the naphtha Were not flashed from the crude oil and the preheated whole crude oil were to the bottom of fractionating tower lS i, the temperature of the lower portion of the fractionating tower would be lowered, the temperature of the mixed residuum stream in line 166 would be lower and more heat would be required from heater or furnace 168, that is, a larger and mose costly furnace would have to be used. At the same time, if the naphtha were not flashed from the crude oil there would be too much heat in cracking reactor 134 because of the high feed preheat temperature and high carbon burning rate and it would be necessary to remove heat from this reactor 134.

The invention is not to be restricted to the actual designs given in Figs. 1 and 2 but can be used in similar integrated combination units wherein a Whole crude petroleum oil is preheated by heat exchange with one or more different process streams and flashed to remove naphtha which is passed to a catalytic cracking zone to control the temperature therein While reforming the virgin naphtha. Instead of using the usual bubble tower fractionating tower: other fractionating means may be used. Hot catalytically cracked products are used to remove lower boiling hydrocarbons to produce a residuum having an initial boiling point of about 1100 F. which is preferably coked as above described to produce gas oil preferentially rather than gasoline such as a visbreaking operation and the hot coker products are then passed to the catalytic cracking reactor as part of the feed to crack the coker gas oil to gasoline to reform coker gasoline to raise the octane number thereof. The residuum or topped crude is either coked or catalytically cracked so that the entire crude oil is converted to extinction.

The dual zone setup in Fig. 1 does not necessarily use coker for cracking the tower bottoms. This could be done in a catalytic cracking unit, such as 174 of Fig. 2. Also, a coker could be used in place of catalytic cracking reactor 174 in Fig. 2. The latter arrangement may be especially important when it is necessary to condense some of the heavy ends in the coker overhead to prevent contamination of catalyst in the catalytic cracking reactor.

In Fig. 1 it may be advisable to remove some of the metals and heavy ends from the coker overhead before it enters reactor 22 so as to prevent catalyst contamina tion. This may be accomplished by any of several well known methods, such as a liquid scrubber or a bed of solids of adsorbent nature or at a suitably lower temperature than the coking reactor to condense the desired amount of heavy ends.

What is claimed is:

1. A process for converting hydrocarbons which comprises flashing naphtha from preheated crude oil, passing the hot flashed naphtha vapor without substantial change in temperature to a catalytic cracking zone, passing at least part of the flashed bottoms to the lower portion of a fractionating zone, withdrawing a bottoms fraction from said fractionating tower and passing it to a second cracking zone maintained at cracking temperature, passing hot cracked vaporous products from said second cracking zone together with said hot flashed naphtha vapor to said catalytic cracking zone, withdrawing a distillate gas oil as a side stream from an intermediate portion of said fractionating zone and passing it to said catalytic cracking zone and passing the total overhead hot cracked vapors from said catalytic cracking zone to the bottom portion of said fractionating zone below the level of introduction of said flashed bottoms to strip out volatile hydrocarbons from said flashed bottoms and to condense out heavy ends from the cracked vapors.

2. A process according to claim 1 wherein said second cracking zone is a coking zone.

3. A process according to claim 1 wherein said second cracking zone contains finely divided solids as a dense fluidized bed.

4. A process according to claim 1 wherein said second cracking zone contains finely divided cracking catalyst as a dense fluidized bed.

5. In a process wherein preheated total crude petroleum oil has its pressure reduced to flash off a hot naphtha cut from a bottoms fraction and the bottoms fraction is then fractionated into a gas oil fraction and a second bottoms fraction and said second bottoms fraction is cracked in one cracking zone maintained at cracking conditions and the gas oil fraction is cracked in a catalytic cracking zone maintained under cracking conditions by the introduction of hot regenerated catalyst and hot cracked vapors from said first cracking zone are passed directly to said catalytic cracking zone in admixture with said gas oil fraction, the improvement which comprises controlling the temperature of cracking in said catalytic cracking zone by introducing said hot flashed naphtha at below cracking temperature into said catalytic cracking zone to absorb some of the excess heat in said catalytic cracking unit.

6. In a process wherein preheated total crude petroleum oil is separated into a gas oil fraction and a bottoms fraction in a fractionating zone and the gas oil fraction is catalytically cracked in a catalytic cracking zone wherein at least part of the heat of cracking is supplied by hot regenerated catalyst from a regenerator and the bottoms fraction is cracked in a second cracking zone and the hot vaporous cracked products from said catalytic cracking zone are passed to the bottom portion of said fractionating zone to assist in the fractionation of hydrocarbons and stripping therein of volatile hydrocarbons and the hot vaporous cracked products from said second cracking zone are passed directly to said catalytic cracking zone, the improvement which comprises passing the preheated crude petroleum oil to a flash zone wherein hot naphtha vapors are flashed 01f from the crude oil and substantially all of the hot naphtha vapors at substantially below cracking temperature are passed to said catalytic cracking zone to absorb some of the heat from the mixture undergoing cracking, and the bottoms fraction from said flash zone Without heating or cooling is passed to the bottom portion of said fractionation zone above the point of introduction of the hot cracked products from said catalytic cracking zone whereby low boiling hydrocarbons are stripped out from said bottoms fraction from said flash zone and higher boiling components are condensed from said cracked products to form said first bottoms fraction.

7. A process according to claim 1 wherein said second cracking zone is a catalytic cracking zone containing cracking catalyst of much lower activity than the catalyst in said first mentioned catalytic cracking zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,310,317 Roberts Feb. 9, 1943 2,388,055 Hemminger Oct. 30, 1945 2,644,785 Harding et a1. July 7, 1953 2,739,929 Madinger Mar. 27, 1956 2,763,600 Adams et al Sept. 18, 1956 

